....
Yeah, that's what some of them just might do, actually. But I guess there's a reason why they invested in GBTC shares, rather than buying the coins directly: They like the type of investment vehicle, with all its disadvantages and advantages. And that's the very reason they may just stay in that vehicle!
but in the meantime they have learned how to use a Trezor or a Ledger hardware wallet and now feel comfortable being totally in control of their own money. They probably are cluey enough and incentivised to do so ...